He could in the sense that he can hit harder than Marquez ergo landing a counter of that nature would put Pacquiao out. He would KO Pacquiao at least not in that manner because he would never commit to a punch the way Marquez did.

JMM walked thru hell to get that KO. Floyd would have not taken the risks JMM did in order to get that KO. Floyd is a safety first fighter who does not fully commit to or sit on his punches unless he has his opponent in serious trouble